Parasite On My Brain
by The Linn
Summary: Well, what happens when Reid gets a Yeerk? Weird stuff, that's what. I'm just going to make it rated T ahead of time, 'cause I know it's going to get there. I own nothing! CROSSOVER BETWEEN CRIMINAL MINDS AND THE BOOK SERIES, ANIMORPHS.
1. Chapter 1

**Hello, my pretties! I am writing in a peculiar place: my bedroom! I'm using my family's very VERY old laptop to type this and let me say, it is quite painful. I have been sitting here for… 15 minutes now and I've gotten this much down. Whatever, I'll have you know that I am a HUGE fan of the old book series **_**Animorphs**_**, and this idea came to me while I was in Church. (I have almost every single book in the series; I am still searching for a few more!)Haha, here we go!**

It seemed like a normal morning at the BAU. Dr. Spencer Reid walked in, looking normal with his geek-ish clothes and messenger bag slung over his shoulder. No one gave him a second glance; he seemed normal- well as normal as the genius could be. Little did they know what had happen to their resident genius over the weekend. Lurking inside the skull of one Spencer Reid was a parasite, one not of this Earth.

It was a yeerk.

The real Spencer Reid had no control over his body. The alien parasite wrapped around his brain did. A prisoner in his own head, Reid could not reach out for help. He tried to move his legs, turn the other direction and run, but he couldn't. He tried to open his mouth to yell, tell the world that there was something controlling him, even if they thought he was crazy. He still couldn't. Reid couldn't twitch his own eyebrow, blink his own eye, or tap his own foot. All he could do was watch and listen as the yeerk passed right by the people who might be able to help him.

He couldn't.

Reid sat down at his desk- well, his body sat down, with the yeerk controlling it. The only form of entertainment the real Reid had was listening to the yeerk's bloated ego.

"_Haha! Foolish humans! You will all fall subject to the mighty Yeerk Empire soon!_" It screeched inside Reid's head, the only ones hearing it being Reid and itself.

"_Will you SHUT UP already?!_" Reid yelled at it. All he had heard from the little monster had something to do with "enslaving the human race". It was taking a mental toll on the young genius, thinking that he wouldn't be able to take much more from the egotistical slug. Reid remembered how the alien parasite came into his head. Reid had gotten back to his apartment on Sunday night, exhausted after a long case. And he was still expected to be at the office in the morning. Reid had unlocked his door and stepped inside, shutting it behind him. But before he had gotten any farther into his apartment, a large, scaly hand- more like _claw_- came over his mouth. Reid's eyes grew wide, not sure of who or _what _was attacking him. Reid tried to kick, but he found two large, muscular, and again, scaly arms holding his legs. A similar pair of reptilian-like arms was holding Reid's arms to his sides. Shrill laughter filled his head, confusing Reid. His ears were not picking up any sounds, yet the voice filled his head. Reid was terrified; was he succumbing to schizophrenia like his mother? A light flickered on, and Reid's eyes grew wider- if it was even possible for them to _get _wider. A creature was standing in front of him, with two other of the reptilian monsters by the lead one. The lead creature, who was obviously in charge, was strange. It looked like a combination of different animals. The bottom half looked like a deer, but instead of having brown fur, it was _blue_ fur. And instead of having a cute little fuzzy tail, there was a huge, threatening scorpion-like tail coming off of the creature's backside. At the end of the tail was a menacing looking blade that was slightly tinted red with blood. The top half of the creature was even more disturbing. There was a human-like torso covered in blue fur coming from the front of the creature, like a mythical centaur. Two muscular arms came from the torso, but they had too many fingers. The head was the most frightening to Reid. It had two, almond shaped eyes, a flat nose with four slits, and _no mouth_. Mounted atop the head were two eyes on stalks, swiveling around to look at its troops. The reptilian monsters were a completely different story. There were quite tall, no doubt reaching seven feet tall. They had muscular bodies covered in scales, complete with a snake like tail. Coming from the ankles, knees, tail, wrists, elbows, and head of the monsters were sharp blades that could easily slice Reid to pieces. Their heads were menacing, with sharp, jagged teeth jutting out of their muzzles. They had cold eyes, looking at Reid, ready to take away his life in an instant. But underneath the cold-blooded looks, Reid could tell by their body language that they were terrified at the moment. By looking at the way they glanced with fear at the blue-deer creature, Reid could tell that the deer creature was what they were terrified of.

"So, human!" A booming voice filled Reid's head. "Are you ready to bow down to your Yeerk masters?" Reid saw none of their mouth's moving, but by the way the deer-creature moved, Reid could tell it was coming from him. But the creature had no mouth!

_He's speaking telepathically to me! _Reid thought. _You idiot! That's impossible! This whole situation is impossible!_

The deer creature smiled with his eyes. "I am Visser Three!" it said, Reid could tell he had a blown up ego by the way he said he own name. "I am the leader of the Yeerk invasion on Earth, and you will be receiving your Yeerk now, Doctor Reid!" Reid's jaw dropped as far as it could behind the scaly monster's claw.. The creature, Visser Three, knew Reid's name! Before Reid could do much more, he was yanked over to a tank filled with some type of sludge. Before Reid could resist, his head was thrust into the sludge. Reid was panicking, what did Visser Three mean that he was receiving a _yeerk_, and what was a yeerk in the first place? Something slimy was starting to crawl in Reid's ear, forcing its way through his ear canal. Reid tried to shake his head, get the thing out of his ear, but the muscular arms kept his head firmly in place. The thing made its way through Reid's ear canal, until it reached his brain. It wrapped itself over Reid's brain, receiving all of Reid's memories, but at the same time Reid was receiving the thing's memories. Reid knew that the thing that had wrapped itself around his brain was a parasitic alien called a yeerk. He knew that the reptilian monsters were aliens called Hork-bajir, and that Visser Three was an alien called an Andalite. He knew the history of the Yeerks, about how the Andalites fought the Yeerks, and how the Yeerks were attempting to enslave the human race. He knew about the Andalite bandits who were fighting the Yeerks off Earth. Reid tried to move his body, and couldn't. The yeerk controlled him now.

**Just heard that Neil Armstrong died… I'm very sad! Anyways, I'll update soon, by the end of the night! Until then, my fine furry friends!**

**-The Linn**


	2. Chapter 2

**Welcome back! I plan on having an interesting chapter, you're going to find out that yeerks have quite colorful vocabularies! Anyways, this'll be a fun chapter, I promise! We're going to get a little bit of Reid-whumpage in this chapter, and Morgan _might _get hit upside the head by a certain gorilla…**

**WORDS SURROUNDED BY THESE: […] ARE THOUGHT SPEAK.**

The yeerk sat at Reid's desk. It was early, virtually no one else was there. Morgan walked in, obviously exhausted.

"Hey Pretty Boy. How come you don't look like hell, like the rest of us?" It was true. While Morgan, Hotch, Rossi, Emily, JJ, and Garcia all looked horribly tired, Reid looked ready to go, full of energy. In reality, it was just the Yeerk. It was full of energy when it awoke, ready to go start its part in enslaving the human race. But instead of answering in the freaky truth, the Yeerk lied. It quickly flipped through Reid's memories, figuring out how to answer Morgan's question.

"Don't know. Got a good night's sleep, had some coffee." The Yeerk replied casually, using Reid's voice to deceive Morgan. Morgan shook his head, then turned to go get some coffee. The Yeerk grinned, its ego growing larger by the second. If Reid had control of his eyes, he would have rolled them. The rest of the team slowly filed in, barely anyone other than their team being there. They all walked by a seemingly cheery Reid, mumbling their hellos as they walked to their separate offices and desks. The Yeerk figured he should start doing paperwork to not look suspicious. Using Reid's genius, the Yeerk began to fly through the paperwork, just like Reid always did. Figuring that he should start doing something, Reid started talking to the parasite in his head.

"_So, what's your name?_" Reid thought, knowing that the Yeerk could hear him.

"_Well, puny human, I am the mighty Jenret 473._" The Yeerk sneered back at Reid.

"_Cool name._" Reid replied, even though he couldn't care less about the slimy little alien in his head.

"_That is correct, worthless-_"Jenret was cut off by someone snapping their fingers in front of Reid's face. It was Morgan.

"Yoo hoo, Earth to Pretty Boy! Can you hear me in there?" Morgan asked. Jenret quickly consulted Reid's memories, and then answered.

"Yeah," Jenret said, "What do you need?"

"Nothing. You were just sitting there with this odd expression on your face and it was creeping me out." Morgan said, leaning back with a coffee mug in hand. "And you haven't had any coffee today. What's up with that?"

Jenret started to panic a bit. He didn't know how to answer, so he settled with an obvious lie.

"I was just thinking, kind of forgot to get some." He said casually, Morgan's eyebrows shot up.

"Is that so?" Morgan said, obviously not believing it. But Jenret did not pick up on his disbelief.

"Yup!" Jenret said, smiling brightly, "I was actually about to-" Jenret was cut off by a loud scream coming from outside the glass doors of the BAU. Coming out of the stairwell was what seemed like a circus. A tiger, a grizzly bear, a wolf, a gorilla, a hawk, and a mysterious blue centaur-like creature came bursting out, heads swiveling. The gorilla looked in the glass doors and raised a large finger to point directly at Reid. Jenret started to panic; he knew that the animals were actually the infamous "Andalite Bandits". He started to turn and run, but the "Bandits" were already on top of him. Reid's eyes should've looked panicked, he should've been screaming for help. But Jenret forgot. He stared with hatred at the animals that had him pinned down.

"Fucking Andalite Bandits! You will regret the day you set your shitty hooves upon this planet!" Jenret yelled at them, anger and hatred burning in his eyes. By now the entire team and everyone else in the office was watching in shock, waiting for Reid to be mauled by the wild animals.

"What the hell!" Morgan was yelling. The Tiger, named Jake, who was the leader of the ragtag bunch, looked over at the Gorilla, Marco. Jake nodded, so Marco turned and planted two meaty hands on Morgan shoulder's, looking into his eyes.

[Sir, I need you to calm down. You do not understand what is going on with your buddy over there.] Marco told him in private thought speak, so only Morgan could hear, trying to calm the frantic agent down. Morgan froze. Was the Gorilla talking to him telepathically?

Meanwhile, the Hawk, Tobias, and the Andalite, Ax, were making sure no one intervened while the others restrained a frantic Reid, who was still yelling and cursing at them. The grizzly bear, Rachel, and the wolf, Cassie, were holding Reid's arms and legs down. Jake stood with one paw on Reid's chest, looking straight into his eyes.

[You are coming for us, Yeerk]! Jake spat in public thought speak, so everyone in the office could hear. [For you, Doctor Reid I believe it is, I am sorry but we must starve the Yeerk out of your head. I know you can not answer, but I hope you understand.]

"_I understand!_" Reid thought happily. They were going to get the Yeerk out of his brain.

"NO!" Jenret screamed. "You filthy Andalites will die! I will personally torture you until your fucking minds crack and you dive into insanity!"

Rachel, grab him. Jake ordered the large bear. Nodding, Rachel wrapped a kicking and cursing Reid into a literal bear hug. She marched out of the BAU, with Ax, Tobias, and Cassie following. Marco was still attempting to calm down Morgan. Seeing that he was not giving up, Marco gave the dark-skinned agent a gentle bump on the head, which easily knocked him out. It wasn't going to hurt to much, just knock him out for enough time that they could escape. Laying him gently on the floor, Marco turned and followed the others out. Jake was still in there. He turned to address the entire BAU.

[We are quite sorry that we have to take your agent, but he has been infested with a Yeerk and is in too high of a position to not have it starved out of his skull immediately. He will return in three says, when the Yeerk has been killed. I promise you, but please do not alert the media about this. It will make everything worse, for the Yeerks have people everywhere. If you tell them, the Yeerks will in no doubt infest you also. That will make my job even harder, so please, keep this to yourselves. I do not want to have to come back and starve the Yeerks out of each and every one of you. Thank you.] Jake promptly turned and walked out of the BAU, tigers paws clicking on the tile. He disappeared down the stairwell, leaving the BAU in shock.


	3. Chapter 3

**I am back again, for some late night writing! I'm very happy that I am now allowed too use the good old family laptop from… the dark ages. But since I now can, I will be writing a lot more now because I can get the seclusion I love to write in more. Also, I almost BEG of you to have a basic knowledge of the book series _Animorphs. _It'll make it easier for me so I don't have to stop and explain CONSTANTLY. Whatever, here's Chapter 3! (There might be a little bit of Reid-whump in this chapter.)**

The BAU stood in shock. Morgan began to come around, rubbing his head and sitting up. He chuckled a bit.

"Hey guys, I just had the weirdest dream. A bunch of telepathic animals came in here and kidnapped Reid, claiming they needed to starve something out of his head!" Morgan laughed, but stopped as he looked around at the grim faces of the BAU, minus their resident genius. "Wait… did that really just happen?" Nods came from around the room as they stood in a tense silence.

"What was Reid yelling about?" Prentiss broke the silence after a few minutes. "I mean, that definitely did not sound like Reid. 'I will personally torture you until your fucking minds crack and you dive into insanity'? That doesn't sound even remotely like anything Reid would ever say!"

"Prentiss is right." Hotch said, nodding. "We should consider that possibility that what the, uh, tiger said was true."

Morgan looked at Hotch like he had put a dress on and started singing Top 40 hits in a high pitched voice. "You can't be serious, Hotch!" He almost yelled, frustrated at how ridiculous Hotch was being. Hotch shook his head.

"I say we wait the three days out. Now I'm not saying that we don't look for Reid, but we should keep this within the BAU." Nods of agreement came from around the room. "Good, now everyone get to work!"

**CMCMCMCMCMCMCMCMCMCMCMCMCMCM CMCMCMCMCMCMCM**

Shortly after they reached the stairwell, the Animorphs, as they called themselves, decided it would be best if their captive was not constantly kicking and screaming. Marco gently bumped him on the head, just like he did with Morgan. They quickly descended the stairs, meeting a familiar face at the bottom.

[Erek.] Jake said, acknowledging the young man. Erek was a Chee, a race of advanced androids that came to Earth around the time Moses was still wandering the desert. They had hologram projectors so they could blend in with human society, taking the form of one persona, letting them slowly age and die, then take on a new one. Erek's current persona was a young man in high school

"It will be easier if you all demorph." Erek said, looking at them all. They all nodded, demorphing.

Jake's sleek tiger form turned into the body of a sophomore in high school, with brown hair and eyes, tall with a slight build.

Rachel's large bear morph transformed back into her own, beautiful with blond hair and blue eyes.

Marco's beefy gorilla became a slightly short kid with long brown hair that could use a cut and very tan skin.

Cassie became a dark-skinned girl with short hair and deep brown eyes, keeping a careful eye on her surroundings.

Ax was the only one not demorphing, being the odd one out in the group. While all the others were human teenagers, he was the only actual Andalite of the infamous "Andalite Bandits". Ax was also a teenager, so he morphed into the strangely gorgeous kid that came from combining everyone else on the team's DNA.

Then there was Tobias. See, there is a curse that comes along with the ability to turn into any animal that you touch. If you stay in a morph for more than two hours, you become stuck in that form. That's what happened to Tobias. He became stuck in the body of a red-tailed hawk. But an all-powerful being, called the Ellimist, gave him his morphing powers back and the power to morph back into his human self. He just perched on Erek's steel shoulder, watching the others.

Once everyone was ready, Erek picked up the limp Spencer Reid. He projected a hologram over himself, Reid, and Tobias that looked like a business man talking furiously on a cell phone. Walking out of the stairwell, the easily walked out of the FBI Headquarters. Outside, Erek's "father", who was really just another Chee, was waiting in a van. The all hopped in, and quickly drove away. They drove for a while, everyone silent, thinking about how they had kidnapped a Yeerk-infested FBI Agent. They reached a forest and went off road, bumping up and down. They arrived at a old cabin after fifteen minutes of off-roading. They hurried inside, sitting Reid gently down in a chair that was in there. They tied his arms and legs down so when the Yeerk in his head awoke, it would not escape. Ax demorphed to his true form, they thanked their Chee friends, who then left. They all began to talk about how crazy the next couple days would be.

"Do you think they'll listen and no go to the news stations?" Jake asked the others.

"They're a smart bunch," Cassie said, "I think they'll listen."

"Yeah, but what if they don't?" Marco asked. "Then they go on a manhunt, find our little cabin here, and we're all screwed." Rachel punched him on the arm, causing him to yelp in pain and grab it,

"But that's not going to happen, idiot. I have faith in them." She said. Just then, a groan came from the chair behind them. Reid, both the Yeerk and the real Spencer Reid, were waking. They were both shocked when they saw the captors/saviors. The Yeerk was infuriated that the Andalite Bandits were actually a bunch of human kids and one Andalite kid. Reid was surprised, but nonetheless thankful for them. After that, the Yeerk began to curse and scream and yell.

"It's no use, Yeerk." Marco yelled over to him. "No one can hear you out here."

**Well, I came up to my room to write at 5:00 PM. It is now 1:08 AM. Geez, people, but I'm still going to write! Next chapter will most likely be the last, but I might do another one.**


	4. Chapter 4

**Hello, my fine readers! I know I should sleep, but I have way too many brilliant ideas circling around in my head, so I just grabbed a Red Bull, and I'm ready TO FREAKING GO! (My hands are shaking right now, sorry for typos)**

Three Days Later

Reid was suffering, the past few days left him in so much pain. He would say that the pain rivaled Hankel, the anthrax, and getting shot in the knee. The Yeerk in his skull was dying, it was horrible. Both he and Jenret were crying out in pain. From being observant, he had learned his saviors/captor's names. There was Jake, the leader, Marco, the joker, Rachel, the warrior, Cassie, the caring, Tobias, the accident, and Ax, the alien. But Reid was surprised when Marco came in, morphed as a gorilla, and bumped Reid on the head. What were they doing in Jenret's final hours? He asked himself as he went into the darkness of unconsciousness.

Erek and Erek's father came into the sad little shack and took Reid outside to where the van was waiting. They all piled in once again, driving back into Quantico after off-roading again. They pulled up outside the FBI Headquarters, preparing to return Reid right as the slug in his skull died. Ax morphed to his human form, Tobias once again perched on Erek's shoulder, and Erek picked up Reid and through up the same business man. They walked inside, only getting a second glance from anyone wondering why a bunch of high schoolers were in the FBI Headquarters. They walked up the stairwell, stopping right outside the sixth floor door. Erek handed Reid, who was slowly regaining consciousness, to Jake and Ax, who put his arms around their shoulders. They all took a deep breath to calm their nerves, then pushed the door open. Rachel, Cassie, Marco, Erek, and Tobias led the way. About the time they pushed open the glass doors, Reid and Jenret regained consciousness. And once again, they both began screaming in pain. That alerted the BAU to their arrival.

"Reid!" Morgan yelled, jumping over desks to get the man who considered too be his little brother. Before Morgan could reach the screaming genius, Erek stopped Morgan, placing an arm against his chest. Morgan couldn't move the seemingly normal kid, but kept struggling to get closer.

"I can not allow you to interfere right now. The Yeerk in your friend's head is in the final stage of death, if you do something the death might spread to your friend also." Erek told the infuriated Morgan in an icy voice.

Just like they had a few days before, the BAU watched in a shocked silence as their colleague screamed in pain. JJ and Garcia were crying, Morgan was attempting to push past the unnaturally strong kid, Hotch and Rossi were watching in a concerned silence, and Prentiss was trying not to burst out in tears. It went on for a few minutes, Jake and Ax had already placed Reid on the ground, where he and Jenret writhed and howled in hurt. Then, one last scream pierced the air, and there was quiet. Only then did Erek let Morgan and the rest of the BAU pass, where they all rushed over to watch in horror as a slug-like creature dropped out of Reid's ear. Reid's eyes had been clinched shut, but they loosened, and he slowly opened them under his own free will. A goofy grin washed over the genius' face, and he started to laugh. Standing up slowly, he walked passed his puzzled team mates and hugged Jake, who was near by.

"Thank you, thank you so much…" Reid laughed out.

"It was my pleasure, Doctor." Jake replied, patting the man on the back. Reid withdrew, walking away.

"Where you going, kid?" Morgan yelled after him.

"I haven't had a cup of coffee in three damn days, Morgan!" Reid replied, making a bee line towards the break room, leaving the BAU to laugh. But it died down as they turned to analyze the strange teenagers that saved their youngest member from… whatever it was they saved him from, they still weren't entirely sure.

"Like to explain what's going on, kids?" Hotch asked, one eyebrow raised. Jake cleared his throat and stepped forward.

"Well, uh, I'm Jake, the _unofficial _leader of this group," Jake said, stressing the word unofficial with a glare to Marco, who was snickering. "I, uh, was the tiger you saw the other day." That made a lot of eyebrows shoot up from the BAU members.

"Is that so?" JJ asked, not believing.

"Uh, yeah. Marco here was the gorilla, and he better apologize for knocking that one guy out when we left." Jake said, glaring at Marco, who muttered sorry. "Cassie was the wolf, Rachel was the bear, Tobias… well as you can see Tobias was the hawk, and Ax here was the weird blue deer thing."

"Andalite." Reid said, walking back with a cup of coffee in hand. The BAU could see the usual way-to-much sugar in the cup.

"Right. Well, uh, we should get going. Ax, go back to your natural form, and everyone go to bird forms. Erek, meet us back at the barn." Jake said, and everyone started doing as they were told. Once again, the BAU was silent, watching in horror and amazement as the kids were replaced with birds. Reid walked over to a window and opened it.

"Come by if you ever need any help." He told them as they flew out the window.

[Will do, Doctor!] Jake called back.

**Well that story was completed in… 17 hours, six of those hours I spent sleeping, and many others were spent working on other stories or reading other stories. Anyways, I'll try to finish up my last uncompleted story soon, but until then good bye!**

**-The Linn**


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